This study is a phase 2, multicenter, randomized, double-blind, active placebo-controlled trial of AMG 479 or placebo in combination with gemcitabine as first-line therapy for locally advanced unresectable adenocarinoma of the pancreas. Approximately 150 subjects will be randomized in a 1:1 ratio to AMG 479 and gemcitabine, or gemcitabine and placebo. Randomization will be stratified by ECOG (0 or 1).